Parkinson's disease belongs to a group of conditions called motor system disorders, which are the result of the loss of dopamine-producing brain cells. The four primary symptoms of PD are tremor, or trembling in hands, arms, legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination. As these symptoms become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks. Other symptoms may include depression and other emotional changes; difficulty in swallowing, chewing, and speaking; urinary problems or constipation; skin problems; and sleep disruptions. There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic PD, and diagnosis is based on medical history and a neurological examination.
Currently, there is no cure for PD, but a variety of medications provide relief from the symptoms. Usually, affected individuals are given levodopa combined with carbidopa, which delays the conversion of levodopa into dopamine until it reaches the brain. Nerve cells can use levodopa to make dopamine and replenish the brain's dwindling supply. Although levodopa helps at least three-quarters of parkinsonian cases, not all symptoms respond equally to the drug. Bradykinesia and rigidity respond best, while tremor may be only marginally reduced. Problems with balance and other symptoms may not be alleviated at all. Anticholinergics may help control tremor and rigidity. Other drugs, such as bromocriptine, pramipexole, and ropinirole, mimic the role of dopamine in the brain, causing the neurons to react as they would to dopamine. An antiviral drug, amantadine, also appears to reduce symptoms.
An estimated 53 million people have PD resulting in about 103,000 deaths globally. Parkinson's disease typically occurs in people over the age of 60, with males being affected more often than females. The average life expectancy following diagnosis is between 7 and 14 years. Parkinson's disease is typically idiopathic (having no specific known cause); however, a proportion of cases can be attributed to known genetic factors. For example, mutations in specific genes have been shown to cause PD (e.g., alpha-synuclein (SNCA), parkin (PRKN), leucine-rich repeat kinase 2 (LRRK2), PTEN-induced putative kinase 1 (PINK1), DJ-1 and ATP13A2). Mutations in LRRK2 are the most common known cause of familial and sporadic PD, accounting for approximately 5% of individuals with a family history of the disease and 3% of sporadic cases. The LRRK2 G2019S gain of function gene mutation is one of the most prevalent mutations contributing to PD pathogenesis. While treatments for PD are available, more effective therapies are needed.